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<head>
  <meta charset="UTF-8">
  <title>Title</title>
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<body>
login fail
原来model的值: <span th:text="${username}"></span><br>
重定向传过来的值: <span th:text="${param.redirect_msg}"></span><br>
flash，只显示一次: <span th:text="${flash_msg}"></span><br>
</body>
</html>